Building energy modelling and simulations: qualitative and quantitative analysis

Transcription

1 MATEC Web of Conferences 7, 0005 (207) DOI: 0.05/ matecconf/ XXVI R-S-P Semnar 207, Theoretcal Foundaton of Cvl Engneerng Buldng energy modellng and smulatons: qualtatve and quanttatve analyss Robert Gajewsk,*, Paweł Penążek Warsaw Unversty of Technology, Faculty of Cvl Engneerng, Al. Arm Ludowej 6, Warsaw , Poland Abstract. Buldngs consume half of all energy use and are also responsble for a smlar proporton of carbon doxde emsson. The heat transfer across the buldng envelope - the shell of a house that separates the nsde and outsde, should generally be mnmzed. In the paper valdaton and verfcaton based on Buldng Energy Smulaton Test (BESTEST) of Energy3D computer code s presented. Program proved to be an excellent tool for qualtatve and quanttatve analyss of buldngs. Introducton and lterature revew Buldngs consume between 40% and 60% of all energy use. They are also responsble for a smlar proporton of humanknd s carbon doxde emssons. In the frst part of twenteth century, calculatons of the thermal response of buldngs have made an assumpton that the boundary condtons and the whole problem are statc. Thus a fcttous steady-state problem was defned n order to perform energy calculatons. Now buldng energy modellng s manly based on CFD (Computatonal Flud Dynamcs) methods. An excellent revew of dfferent modellng methods for energy n buldng s gven by Underwood and Yk n ther book []. Energy smulaton n buldng desgn s presented by Clarke n [2]. Buldng performance smulaton for desgn and operaton are descrbed n the monograph [3] edted by Hensen and Lambers. Revew of dfferent buldng smulaton applcatons can be found n [4] and [5]. Practcal approach to computatonal flud dynamcs, whch s sutable for cvl engneers, can be found n [6]. A practcal gude of fnte element methods for computatonal flud dynamcs can be found n [7]. All computer codes used for buldng energy smulatons especally these based on computatonal flud dynamcs are very complcated. Ther proper usage requres deep theoretcal and practcal knowledge. There are two computer codes Energy2D and Energy3D created by Doctor Cherles Xe whch are very smple and user frendly. 2 Buldng energy theoretcal background The thermal performance of a buldng s represented by the effcency wth whch t uses energy to mantan the thermal comfort for ts occupants. In order to calculate ths energy * Correspondng author: r.gajewsk@l.pw.edu.pl The Authors, publshed by EDP Scences. Ths s an open access artcle dstrbuted under the terms of the Creatve Commons Attrbuton Lcense 4.0 (

2 MATEC Web of Conferences 7, 0005 (207) DOI: 0.05/ matecconf/ XXVI R-S-P Semnar 207, Theoretcal Foundaton of Cvl Engneerng all heat transfer methods are taken nto account: thermal conducton, convecton and radaton. In thermal conducton the rate of heat flow s governed by the followng relatonshp: Q T A () t x where Q s the thermal energy change of the object wthn tme perod of t, T s the temperature dfference across a dstance x, λ s the thermal conductvty of the materal and A s the area. Ths relaton s also known as Fourer s law of thermal conducton n whch we use the concept of heat flux Φ. T (2) x In the process of convecton thermal energy passes through a flow of flud. Convectve heat flux s estmated by smple formula h T T (3) where h s the convectve heat transfer coeffcent of a flud, T s the temperature of the surface and T s the temperature of the flud. Ths equaton s known as Newton s law of coolng. In the radaton process the energy radated by an object per unt tme s proportonal to the fourth power of the absolute temperature 4 T (4) where σ s the Stephan-Bolzman constant, ε s the emssvty of the object s materal. Ths formula s known as Stephan-Bolzman law. Radaton Conducton Radaton Convecton Conducton Convecton Fg.. Heat transfer across the buldng envelope. The heat transfer across the buldng envelope - the shell of a house that separates the nsde and outsde, should generally be mnmzed (see Fg. ). The measure of nsulaton s 2

3 MATEC Web of Conferences 7, 0005 (207) DOI: 0.05/ matecconf/ XXVI R-S-P Semnar 207, Theoretcal Foundaton of Cvl Engneerng named R-value. It represents the ablty to resst heat transfer through the buldng envelope under gven temperature dfference. U-factor on the other hand represents materal s ablty to transfer heat. T2 T UT 2 T (5) R The thermal energy p ganed or lost per unt tme through a surface area A of a buldng component at tme t s: p t AU T n Tout t (6) The total heat flow across the buldng envelope s the sum of heat flow through all of ts components: t t p AU T T (7) The total quantty of heat that flows across the entre buldng envelope n a year s the sum of heat flow through all of ts components over 365 days: 365 N d k n out Q AU T n Touttd k, (8) N where N s the number of tme ntervals n whch a day s dvded for ths calculaton. 3 Verfcaton and valdaton In addton to all errors that can arse whle performng numercal smulaton there are also uncertantes due to mproper modellng of physcs or ncorrect computatonal desgn. Verfcaton and valdaton procedures are used n order to properly assess soluton. Both terms have dstnctve defntons. As stated n [6] verfcaton can be defned as a process for assessng the numercal smulaton uncertanty and when condtons permt, estmatng the sgn and magntude of the numercal smulaton error and the uncertanty n that estmated error. Ths procedure concerns prmarly the nput parameters used for geometry, ntal condtons, and boundary condtons. On the other hand as stated n [6] valdaton can be defned as a process for assessng smulaton model uncertanty by usng benchmark expermental data and when, condtons permt, estmatng the sgn and magntude of the smulaton modellng error tself. Ths procedure smply means valdatng the calculatons by establshng a range of physcal condtons obtaned from the calculatons and by performng comparsons of the results from the CFD code wth experments that span the range of condtons. Both processes were performed for Energy3D code n order to check the qualty of models and results of smulatons. From a valdaton perspectve, comparatve tests wll show that Energy3D gves solutons that are reasonable compared to other energy smulaton programs. Comparatve testng s also useful for nput debuggng. Energy smulaton programs have so many nputs and outputs that the results are often dffcult to nterpret. In order to compare results wth known from lterature Buldng Energy Smulaton Test (BESTEST) was used. It was descrbed n many publcatons [8], [9], [0], [] [2] and [3]. Sample BESTEST buldng s shown n Fg. 2. The tests descrbed n ANSI/ASHRAE Standard , Standard Method of Test for the Evaluaton of Buldng Energy Analyss Computer Programs (ANSI/ASHRAE 200) were performed. 3

4 MATEC Web of Conferences 7, 0005 (207) DOI: 0.05/ matecconf/ XXVI R-S-P Semnar 207, Theoretcal Foundaton of Cvl Engneerng Fg. 2. BESTEST case buldng 600. The basc test buldng s a rectangular sngle zone (8 m wde x 6 m long x 2.7 m hgh) wth no nteror parttons and 2 m 2 of wndows on the south exposure. The buldng s of lghtweght constructon wth characterstcs as descrbed below n Table. Table. Wall Constructon (lght weght mass). Element k [W/mK] Thckness [m] U [W/m 2 K] R [m 2 K/W] Densty [kg/m3] c p [J/kgK] Int. Surface Coeff Plasterboard Fberglass Qult Wood Sdng Ext. Surface Coeff Overall, ar-to-ar Charts comparng Energy3D results wth other whole buldng energy smulaton programs are n Fg. 3. More results can be found n B.Sc. thess prepared by Penążek [4]. 4 Qualtatve and quanttatve analyss Energy3D can be used for both qualtatve and quanttatve analyss. One can measure and compare such values as: Effects of the house sze on the energy use; Effects of the house shape on the energy use; Effects of roof nsulaton on the energy use of a house; Effects of roof colour on the energy use of a house; Effects of solar heat gan coeffcents of wndows on the energy use of a house; Effects of orentaton on the energy use of a house; 4

5 MATEC Web of Conferences 7, 0005 (207) DOI: 0.05/ matecconf/ XXVI R-S-P Semnar 207, Theoretcal Foundaton of Cvl Engneerng Effects of the thermostat settng on the energy use of a house; Energy use of a house at dfferent locatons; Effects of envronment albedo on the energy use of a house; Effects of sun-facng wndows on the energy use of a house; Effects of trees on the ar condtonng of a house; Fg. 3. Comparson of Energy3D results wth other whole buldng energy smulaton programs. Results presentng energy use of a house at dfferent locatons are n Fg. 4. Dfferences n clmate n Poland are relatvely small but annual energy for Bałystok (sold lne wthout markers) and Wrocław dffer sgnfcantly (qualtatve analyss). Fg. 4. Annual energy for sample buldng located n Bałystok and Wrocław. 5

6 MATEC Web of Conferences 7, 0005 (207) DOI: 0.05/ matecconf/ XXVI R-S-P Semnar 207, Theoretcal Foundaton of Cvl Engneerng 6 Fnal conclusons Ths paper presents valdaton and verfcaton of Energy3D code used for buldng energy modellng and smulatons. Ths smple computer code proved to be an excellent tool for qualtatve and quanttatve analyss of buldngs. Such a program can be an excellent part of a computer supported desgn envronment [2] whch takes nto account also energy consderatons. Ths research was not sponsored by any grant or authortes. Ths research was done just for pleasure and satsfacton. References. C. Underwood, F. Yk, Modellng Methods for Energy n Buldngs, edton (Wley- Blackwell, Oxford Malden, MA, 2004) 2. J. Clarke, Energy Smulaton n Buldng Desgn, 2 edton (Routledge, Oxford, 200). 3. J. L. M. Hensen and R. Lamberts, edtors, Buldng Performance Smulaton for Desgn and Operaton (Routledge, London; New York, 20) 4. M. Barater, V. Corrado, A. Gasparella, and F. Patuzz, edtors, Buldng Smulaton Applcatons BSA 203 (Bozen-Bolzano Unversty Press, Bozen-Bolzano, 203) 5. M. Barater, V. Corrado, A. Gasparella, and F. Patuzz, edtors, Buldng Smulaton Applcatons BSA 205 (Bozen-Bolzano Unversty Press, Bozen-Bolzano, 205) 6. J. Tu, G. Heng, C. Lu, Computatonal Flud Dynamcs, Second Edton: A Practcal Approach, 2 edton (Butterworth-Henemann, Amsterdam, 202) 7. D. Kuzmn, J. Hamalanen, Fnte Element Methods for Computatonal Flud Dynamcs: A Practcal Gude (SIAM, 204) 8. R. H. Hennnger, M. J. Wtte, EnergyPlus Testng wth ANSI/ASHRAE Standard (BESTEST) (Lawrence Berkeley Natonal Laboratory, Berkeley, Calforna, 2004) 9. R. Judkoff, J. Neymark, Internatonal Energy Agency Buldng Energy Smulaton Test (BESTEST) and Dagnostc Method (Natonal Renewable Energy Lab., Golden, CO (US), 995) 0. R. Judkoff, J. Neymark, Standard Method of Test for the Evaluaton of Buldng Energy Analyss Computer Programs (Amercan Socety of Heatng, Refrgeratng and Ar-Condtonng Engneers, Inc., 2004). R. Judkoff and J. Neymark, n (Chambery, France August 25-28, 203, 203). 2. M. Woloszyn, C. Rode, IEA Annex 4, MOIST-ENG Subtask Modellng Prncples and Common Exercses (2007) 3. T. Soubdhan, T. A. Mara, H. Boyer, A. Younes, World Renew. Energy Congr. VI (Pergamon, Oxford, 2000) 4. P. Penążek, Computer Smulaton of Buldng Energy (B.Sc. Thess, Warsaw Unversty of Technology, Faculty of Cvl Engneerng, 206) 6